40' Tall Warehouse Column Design 1

[JNEnginr]

Hey everyone, Happy New Year!

I'm looking to design an addition to an existing warehouse. 90ftx350ft. Exterior Walls will be 40' tall Tilt up Precast Concrete. Roof is metal deck on steel bar joists supported by steel joist girders supported by columns. What I'm debating is the interior columns. My first thought is steel columns. However, this warehouse actually already had a large addition put on it, and it utilized concrete columns instead, with girders sitting atop the columns. In some other areas, steel girders were supported by brackets precast into the concrete columns.

Can I get some feedback on typical warehouse construction? I'm based in Northeast USA. Any recommended books/literature?

My current thoughts:
-Since the walls were precast, maybe they just went with precast columns
-steel lead time was too long, so maybe they went with precast columns
-are concrete columns, or steel columns encased in concrete a fire protection requirement?

Thanks!

 

[JNEnginr]

Here's another pic

 

[jayrod12]

Another thing to keep in mind in warehouses, forklift traffic and damage. Those cowboys driving the forklifts have put holes in columns too often. I always try recommending a concrete pier/column encasement for the lower 1m. So maybe that's another bonus in the concrete column court.

 

[dik]

I'd be looking at HSS columns. Depending on the size, use and occupancy, that will determine the FRR required. Concrete filled columns are great. The use of concrete filled encasement for the lower 3' is a great idea... 30" dia, min. Use real X-bracing, too... What type of foundation? does it accommodate large loads. Generally steel will give you a much lighter building.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JNEnginr]

I agree, encasing the bottom of the columns in concrete is a must.

As for the X-Bracing, do you still use that if you're using Tilt up Precast concrete walls?

Shallow Foundations, 3000PSF.

Anyone else have feedback on this?

 

[driftLimiter]

I would expect at least a 10" sq HSS column for this application. Not sure about the x-bracing comment, but you will want to provide a bracing at the top of the column. Depending on your detail this can be accommodated a few ways. Ideally you get a girder and a beam framing into the join in both directions. If you cant use these members to justify the stability bracing, then some kickers from the top of the column connection that connects to the roof diaphragm can be used.

Shallow foundation at 3000 psf there should be no problem designing a footing (maybe pretty big and thick) to transfer the load. But don't forget to check footing bending and shear because you get a pretty good sized load coming off a comparably small baseplate. Footing thickness is generally a cheaper option to resist bending/shear actions in the foundation around here.

I haven't seen the clients go for the concrete encasement of columns, there are other perhaps cheaper ways to protect the columns, not sure about that.

 

[dik]

I think for Vista Cargo with 40' clear height, the columns were HSS 8x8, if memory serves with about 1000 sq.ft. (25'x40') trib area... No seismic loading... Because of the racking, the columns weren't encased with 'elephant feet'.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[driftLimiter]

Quick look at table 4-4 of AISC SCM 15th ed suggests 8x8 can work up to that height as well. My recommendation of 10" sq+ comes from 50'x52' bay spacing with seismic and snow considerations.

 

[JNEnginr]

Hey Everyone,

Wanted to provide an update on this and ask for more feedback. Seems the reason for the concrete around the columns is due to the warehouse requiring a 4hr fire rating.

I feel like i have two options:
-Design the HSS columns for the load, and then just encase in concrete
-Use the steel and the concrete together as a composite column (i image this is cheaper, but would require more detailing)

Anyone have experience in this situation?

Also, are there any sequencing issues I should be aware of? For instance, is the steel column erected, then the concrete placed, and then girders connected to the concrete? Or can the girders just pass through, connected to the steel column, and then those connections are covered in concrete?

Thanks for any and all help.

 

[dik]

4 hours is a bunch... I don't know if you can achieve that with concrete filled HSS. It's not just the columns... it's the rest of the roof. Is the facility sprinklered? Is that a solution? With steel structures, nearly all have been for 2 hour, max. For 4 hours, I'd be looking at concrete.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JNEnginr]

It's definitely class A, maybe the architect misspoke when he said 4 hours.

If you look at the 1st picture i posted, see how the steel girder looks like it frames into the side of the concrete column by sitting on a seat, not the column itself? And if you look at the column on the far left, the concrete keeps going up into the web of the steel girder. There's a seat in that instance as well.

Do you think it's just an extension and it's actually connected to the steel column? And the bolts/plates are just concealed by the concrete?

 

[JNEnginr]

Dik,

Can you clarify what you meant when you said use real X-Bracing?

 

[dik]

I generally use double angle cross-bracing for each 'building' in a large facility, with double lines of support (paired columns). The only time I use 'rigid frames' is for glazing fronts or for loading docks. I occasionally use round BAR stock, but not often.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JNEnginr]

For tall structures as well? Just one big X, 25ft long, 40ft tall? (I'm referencing to previous post)

And if you have glazing, do you find that the moment frames are effective for structures that tall?

 

[dik]

For Vista Cargo, the tallest one I've done, all cross bracing was single 'X'. I think the bays in the short direction were 25' or 30', but don't recall exactly... was a long time back. I did both structures on the site. The large one was five separate structures (independently supported), the lower one being 40' clear height and the upper one being about 30'. It was the first project I did for that company.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JNEnginr]

That's awesome. And so at the locations where the independent buildings met, that's where you did the double lines of support, each I assume having their own X-Bracing. Did the owners just work their layout around the cross bracing? I guess since the bay was so large, they could still pass through it?

I guess you didn't have any moment frames on the 40ft tall one?

 

[jayrod12]

For tall buildings like this you may need to break up the cross bracings with struts along the height to keep the angle size smaller. Otherwise the slenderness recommendations would require some substantial angle sizes to work for a 47 foot long brace. And if they support the cladding at all, then there's no way you're getting the angle cross bracing to work as a single length, but it's uncommon in these types of facilities to have the bracing also support out of plane wind loads.

 

[JNEnginr]

My thoughts exactly on the slenderness. Just an i-beam strut is what i had in mind, so i'd end up with two stacked x's.

 

[dik]

It was a long time back... I don't recall what the bracing was, but it worked, and was not too obtrusive. Bracing was for wind and a light seismic load. I recall checking with a steel supplier on costs for both the bracing and the use of plastic design... and the single x-braces and the plastic design were both less costly. Back then, it was common to do a prelim design of typ framing and have a contractor let you which was more economical. It was purely by accident that I got the work... I dropped in on the firm to see if Gord Gilbert was back from Nepal, and said hi to the structural manager; he asked me if I was interested in taking on a project... this was it. I then spent 10 years there...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik